1. Field of the Invention
The present invention relates to a transport pipe for transporting solid materials such as sand, gravel or concrete. Such transport pipes are combined to form a pipeline such that each individual solid material transport pipe, in the following referred to as pipe, can be removed transverse to the length of the pipeline and replaced by a new pipe without having to pull the pipeline apart in its longitudinal direction. An exchange of pipes is necessary relatively often in such pipelines for solid material transport because the pipes, as a result of the abrasive nature of the transported material, are subjected to high wear loads at their inner side, especially at the transition area between adjacently arranged pipes.
2. Description of the Related Art
The aforementioned known pipes are, in general, provided at their ends with coupling collars which have circumferential grooves at their outer circumference. Clamping shells having a substantially U-shaped or trapezoidal cross-section are then placed into the grooves of the coupling collars of two abutting pipes. These clamping shells are pulled together by clamping or threading means so that in this manner the two pipes can be coupled to one another in a pull-resistant and pressure-resistant manner. Sealing elements can be integrated into these coupling areas, if needed.
The connection of the coupling collars to a single-layer pipe section, hardened at its inner side, is realized such that the coupling collars are pushed by a certain amount over the ends of the pipe section and, subsequently, a fillet weld is produced between the outer surface of the ends and the adjacently arranged end faces of the coupling collar. For this purpose, the ends of the coupling collars facing the pipe section are provided with inner projections by which the coupling collars are correctly positioned at the pipe section.
The manufacture of such a pipe has been performed in the past such that the unhardened pipe sections are produced in overlength cut from a long pipe and then hardened. After hardening, the pipe sections are then cut to the desired length. Subsequently, the coupling collars are welded thereto. This not only results in a relatively high labor expenditure but also frequently in a change of the hardened microstructure of the pipe sections as a result of applying the welding seams. This change is a weak point within the inner wear-resistant area of a pipe in that exactly at the ends which are subjected to greater wear, in particular, when the pipes are angled relative to one another, an additional loading will occur so that the pipes have to be exchanged already after a very short period of use.
Furthermore, pipes are known which are provided with coupling collars that are directly connected as an axial extension of each pipe section and are welded to the axial ends of the pipe section by circumferential V-seams. Such pipes are generally hardened after the coupling collars have been welded to the pipe section, and this results in a relatively great expenditure due to the usually different wall thickness in the area of the pipe section and the coupling collars.
Therefore, it is the primary object of the present invention to provide a solid material transport pipe whose configuration is beneficial in regard to increasing its service life while, at the same time, manufacture and assembly are simplified and the replacement of the pipes is problem-free.
In accordance with the present invention, the solid material transport pipe comprises coupling collars at the ends of a single-layer pipe section, that is hardened at its inner side and has inner wear-resistant layers in the area of the coupling collars. The coupling collars are threaded onto the pipe section.
The gist of the invention is to provide a threading connection of the coupling collars at the pipe section of a solid material transport pipe (in the following simply referred to as pipe). This has the great advantage that no heat is required for connecting the coupling collars to the pipe section so that the already finish-manufactured pipe sections and coupling collars are no longer subjected to disadvantageous effects with respect to the inner wear-resistant layers. Instead, the coupling collars and the pipe sections can be produced completely independently and can then be connected by threading. When needed, suitable adhesives can be introduced into the thread connection for sealing and securing the thread connection.
An especially advantageous embodiment is realized by producing the pipe section of a non-hardenable, pressure-resistant steel pipe, for example, St 37, that is carburized at the pipe interior to a defined thickness and is subsequently hardened. When doing so, a sufficiently thick, radially outwardly positioned wall region is not affected by the carburization and hardening of the inner mantle so that the pipe section, in general, withstands the dynamic and mechanical loading to which a pipe may be subjected.
Pressure-resistant, non-hardenable steel pipes are expediently not hardened together with the coupling collars, but are hardened as overlength pipe sections without the coupling collars and are then filed or cut to the precise fitting length. However, after hardening it is impossible to weld the coupling collars to the steel pipe without losing the previously generated hardness at the inner side (mantle). This is true even when the inner side is cooled. It is possible to connect the steel pipe and the coupling collars by gluing. However, this entails great technical difficulties, especially for pipelines which are subjected to high pressure. According to the inventive configuration, it is now possible to cut outer threads into the soft, non-carburized outer mantle of the pipe section having a hardened inner mantle and, subsequently, the coupling collars are threaded onto the outer thread of the pipe section.
According to a further advantageous embodiment of the invention, the ends of the coupling collars facing away from their end faces are provided with inner threads and the ends of the pipe section are provided with outer threads. The inner and outer threads can be produced at a non-hardened mantle and can thus be manufactured without problems. In this context, it is especially advantageous that for the inner threads at the coupling collars only radially short flanges extending over short partial sections of the coupling collars must be provided. This means that the amount of material needed for the coupling collar can be reduced considerably.
Another very expedient embodiment of the invention resides in that the wear-resistant layers in the region of the coupling collars are formed by rings that are hard at least at their inner side. These rings may extend from the end face of the coupling collars to the area of the threads. The end faces of the ring and of the coupling collars are then positioned in the same cross-sectional planes. The inner diameter of the rings can be smaller than the inner diameter of the pipe section in order to take into consideration the higher wear loads at the transition between two pipes. The hard inner surfaces can be produced by a hardening process. However, it is also possible to have the rings full-hardened. Also conceivable is build-up welding. The rings can also have cast quality.
Moreover, the rings can have a greater wall thickness in the area of the end faces of the coupling collars than in the area of the pipe section. This measure also allows to take into account the higher wear load at the coupling gap between two pipes.
Furthermore, it is possible to provide two such rings adjacent to one another within the coupling collar, wherein the ring having a shorter axial length and positioned directly adjacent to the coupling gap has a higher wear resistance than the neighboring ring which is positioned adjacent to the inner thread. This embodiment also allows for a stepwise reduction of the inner diameter, beginning at the pipe section, continuing via the adjacently positioned ring, and ending with the ring positioned at the end face of the coupling collar.
It is also possible to provide coupling collars having inner threads at their ends facing away from their end faces, wherein the pipe section has outer threads positioned at a spacing from its end faces. In this configuration, the ends of the pipe section can extend past the outer threads to the end faces of the coupling collars. The end faces of the coupling collars and of the pipes section are then positioned in the same transverse planes. In this embodiment, the wear-resistant layers in the area of the coupling collars are thus formed by a hardened inner mantle of the pipe section.
The ends of the pipe section, however, may also end in an area between the end faces of the coupling collars and the outer threads. In this configuration, wear-resistant rings are mounted between the end faces of the pipe section and the end faces of the coupling collars. The inner diameter of the wear-resistant rings is preferably smaller than the inner diameter of the pipe section. The outer diameter of the wear-resistant ring is slightly greater than the outer diameter of the ends of the pipe section. This allows for an enclosure of the wear-resistant rings in the coupling collars.
According to another advantageous embodiment of the principle of the invention, seals are integrated between the coupling collars and the pipe section. These seals prevent reliably a penetration of liquid components of the solid materials to be transported, such as sand, gravel or concrete.
The seals can be integrated in different ways between the coupling collars and the pipe sections. A preferred embodiment proposes that the seals are in the form of O-rings inserted into inner grooves of the coupling collars and supported on the cylindrical outer surfaces at the end of the pipe section which are formed in front of the outer threads. In this embodiment, it is possible that the wear layers within the coupling collars adjoin directly the end faces of the pipe section. Conceivable is also that the coupling collars have inner radial stays projecting radially toward the longitudinal axis and positioned between the wear layers and the end faces of the pipe section.
According to further embodiments, the seal rings are in the form of U-shaped profiles or annular flat packings positioned between the end faces of the pipe section and the wear layers or between the end faces of the pipe section and inner radial stays projecting from the coupling collars into a space between the wear layers and the pipe section. The seals of an annular shape can have a U-shaped cross-section. The legs are then oriented toward the longitudinal axis of the pipes. Moreover, annular flat packings are conceivable. In both cases these seals can be positioned directly between the end faces of the pipe section and the wear layer of the coupling collars, or inner radial stays project from the coupling collars into the space between the wear layers and the pipe section so that the seals are then positioned between the end faces of the pipe section and the radial stays.